I'm going to try to explain this as well as possible but feel free to ask any questions for clarification. I have mountains and plains (picture below) and I'm trying to create a procedural mask that will differentiate between the mountains and the plains by creating a mask vertically along the "Z" axis to pick at what height you want the mask.
You can see an example of what I'm talking about here.
The node setup in that video doesn't work in my instance. How do you achieve this effect?